Heater assemblies for use in ultrapure applications are known in the art. Generally, ultrapure fluids contain some particulates such as dirt, ion exchange resin, and dead bacteria and virus. Typical quantities of such contaminates are 10 to 100 particles per liter of fluid. It is undesirable to allow these contaminates to accumulate. Many of the known heater assemblies include stagnant zones and fluid interstitial matrices that provide potential contamination sites. A fluid velocity drop occurs at the stagnant zones and the stagnant zones tend to accumulate contaminates and/or particulates from the fluid to be heated which are then reintroduced into the fluid flow as slugs of material. When contaminates accumulate in stagnant zones, the geometry of the zones change as particulates and other contaminates accumulate. The change in geometry causes a fluid velocity drop which furthers the accumulation of contaminates. These contaminates can then break loose and travel through the fluid heater to contaminate the fluid and the items such 05 as semiconductor wafers washed by the fluid. Such a construction is not desirable in ultrapure applications such as used in the semiconductor industry where potential contamination of products is unacceptable. For example, known heat exchangers such as disclosed in Dammond, U.S. Pat. No. 2,879,372, or Heron, U.S. Pat. No. 2,809,268, provide non-streamlined tubular flow paths which include tees, recesses and chambers where the element exits which create stagnant zones in the fluid flow that provide potential contamination sites and hence are not well suited for heating fluid in ultrapure applications. Contaminate sites caused by interstitial matrices consist of multiple random surfaces which accumulate contaminates. These random surfaces effect a fluid velocity drop with a resultant increase in the potential for particulate deposition at these site. Tests conducted comparing the cleanliness of the outputted heated fluid from a heater constructed in accordance with the present invention and from conventional, commercially available heaters show a significant improvement in outputted fluid cleanliness when a heater constructed in accord and with the present invention is utilized.